Zawahri fired about 100 shots during his assault, which lasted about 10 minutes, said law enforcement sources who spoke on the condition of anonymity because the case was ongoing.

He fired at passing cars, a bus, pedestrians and police. Authorities have said he had access to more than 1,300 rounds of ammunition.

The semiautomatic weapon used in the rampage appears to have been put together from various parts, possibly in an attempt to circumvent the state’s restrictions on such guns, sources said.

Although certain AR-15-style rifles are banned in California, it’s legal to purchase parts used to assemble and customize the guns. Santa Monica police have said Zawahri used an AR-15-style gun during the attack and was also carrying a .44-caliber handgun.

Sources said detectives are still trying to figure out how the gun was put together and whether Zawahri obtained it whole or assembled it himself.

Zawahri's attack started at his father’s home and ended at Santa Monica College, when police fatally wounded him in the school’s library, police said.

Santa Monica Police Department investigators, working with the Federal bureau of Alcohol, Tobacco, Firearms and Explosives and the California Department of Justice, are trying trace where the weapon parts came from. They are typically available at gun shows as well as on Internet sites and from mail-order catalogs.

California law outlaws commerce in AR-15 weapons that have a magazine capacity of more than 10 rounds, said Garen Wintemute, director of the UC Davis Violence Prevention Research Program. The state also bans specific features of assault weapons, including high-volume detachable magazines, folding, telescopic or detachable stocks or a threaded barrel.

Experts say that buying a legal, already-assembled AR-15, then taking it apart and rebuilding it to custom specifications, is common.

AR-15s can snap apart easily.

Gun control advocates have been raising alarms about illegal weapons that were put together with legally obtainable parts.

The AR-15 rifle was the type of gun used by shooters in an Aurora, Colo., movie theater shooting and at Sandy Hook Elementary School in Newtown, Conn. It’s unclear how exactly those rifles were modified.